MEDIA TALK; A Writer With a Past Turns to Advertising

Ruth Shalit, a former associate editor at The New Republic whose quick rise to prominence as a political reporter was halted by accusations of plagiarism, has found a new calling: advertising.

Last Monday, Ms. Shalit, 28, who left The New Republic at the end of January, began her new job helping to develop ad-campaign strategies at Mad Dogs and Englishmen, an advertising agency in New York.

Ms. Shalit said a main reason she decided to change careers was a realization that the accusations of plagiarism leveled at her in August 1994, and again in June 1995, ''would be a data point about me as long as I stayed in journalism.''

Those accusations were based on a close resemblance between several passages and sentences in articles she wrote and material in articles by other reporters on the same subjects. At the time, Ms. Shalit said she had confused her typewritten notes with articles downloaded from the Lexis-Nexis data base.

The New Republic printed apologies over both incidents, and at the end of 1995, after a critique she wrote about affirmative action at The Washington Post and continued criticism over the plagiarism accusations, Ms. Shalit took a six-month leave of absence.

When she returned in 1996, she moved away from the often-scathing critiques of Washington institutions and people that had earned her a reputation as one journalism's rising stars and a lucrative contract with GQ magazine. Instead, she began writing cultural criticism, book reviews and trend pieces, and maintained a generally low visibility.

But her case drew revived attention last spring when another New Republic writer, Stephen Glass, was found to have fabricated large parts of articles he wrote.

So, Ms. Shalit said, she decided it was time to make a fresh start in ''a field where I could use of all my talents and be judged for who I am instead of on the basis of mistakes I made when I was a dippy 23-year-old.''

Charles Lane, the editor of The New Republic, refused to comment on Ms. Shalit's departure. But Leon Wieseltier, the literary editor, said she had left the magazine of her own accord and expressed confidence that Ms. Shalit had put the plagiarism incidents behind her. ''If I thought that she hadn't paid her dues, I would never have had her write for me,'' he said. MATTHEW J. ROSENBERG